This invention relates to load weighing devices for cranes.
Load weighing devices are intended to measure the weight being carried at a particular instant by the hook of a crane, so that the driver of the crane is able to ensure that the crane is not being overloaded. Such devices generally include a dynamometer which is interposed in the crane rope leading to the hook and which is operable to measure the tension in the rope caused by the load on the hook, and a safe load indicator which is operable to compute the angle of the jib or, in variable-length jib cranes, both the angle and length of the jib in order to supply a signal indicative of the maximum load which the crane can safely carry under the computed conditions of jib angle and length. The signal from the dynamometer is compared either manually or, preferably, automatically with the signal representing the maximum load to ensure that the maximum load is not exceeded. A disadvantage of existing designs is that, due to frictional effects in the various sheaves and to rope bending losses, the dynamometer gives a different reading according to the direction of rope motion.